Bright chromium alloy plating



United BRIGHT CHROMIUM ALLOY PLATING No Drawing. Application March 22,1955 Serial No. 496,067

16 Claims. (Cl. 204-43) This invention relates to chromium-alloycoatings. More particularly, it relates to a method or process ofelectrodepositing coatings of chromium alloys having a bright andlustrous surface, and to the bath used and the coatings producedthereby.

It has been found that suitable trivalent chromium baths can be used toelectrodeposit chromium or chromium alloy plate with a high degree ofsuccess. In U. S. Patent 2,693,444, there has been disclosed achromiumalloy plating bath containing chromium ammonium sulfate,magnesium sulfate, ammonium sulfate, sodium sulfite, salts of alloymetals, ammonium hydroxide, and water. Other baths containing trivalentchromium ions, ions capable of conducting an electric current, and ionsof alloy metals are disclosed in copending application Serial No.487,697. Although the plates acquired by the baths of these twodisclosures vary as to brightness, they must all be mechanically buffedto a considerable extent to obtain a commercially acceptable bright andlustrous finish.

Except as a result of mechanical buffing, no method was previously knownfor producing bright chromiumalloy plates, particularly chromium-ironand chromiumnickel plates. Although many brightening agents have beendiscovered for copper, nickel, zinc, and other plating baths,representative agents of these classes of brightening agents either donot cause chromium-iron or chromium-nickel plate to be brightened, orgreatly reduce cathode efficiency to an intolerable or impossible value.

Buifing of electroplates is a costly operation. Chro mium-iron alloyplate is particularly hard to bull and is excessively costly.

It has now been discovered that by the process and bath of thisinvention, an electrodeposited coating from trivalent chromium baths canbe produced, which overcomes the undesirable features of the prior-artelectroplates.

Accordingly, one of the objects of this invention is to provide asmooth, bright, and lustrous chromium-alloy coat.

Another object is to reduce or eliminate the mechanical bufi'ingheretofore required for brightening chromiumalloy electroplates.

Another object is to provide a method for brightening chromium-alloyplate as it is electrodeposited.

Other objects and advantageous features will be ap-' amides. Bestresults are obtained while using the fol-, lowing organic ammoniaderivatives: methyl pyridium. chloride, diamino pyridine, formamide,urea, dimethyh:

atent Example I An aqueous bath of the following composition wasprepared:

. G./l. Chromium ammonium sulfate [Cr (SO (NH SO -24H O] Ammoniumsulfate [(NH SO 150 Ferrous ammonium sulfate [FeSO (NH S0 -6H O] Methylpyridium chloride 0.5,

The methyl pridium chloride was a supplementary brightening agent. Asteel panel was immersed in the bath as the cathode, while the anode wasconstructed of a chromium-iron alloy Cr, 15% Fe). The bath wasmaintained at a temperature of 115 F., having a pH of from 1.8 to 2.0.The cathode current density was 200 amperes per square foot and theanode current density was approximately 60 amperes per square foot. Thecathode efliciency was 29 percent. The leveling action of the plates wasabout 30 percent per 0.0005 inch of plate. The coating was found tocomprise about 85 percent chromium and 15 percent iron.

The appearance of the resulting plate was mirrorbright and very smooth.

Example [I A bath was prepared similar to that used in Example I exceptthat instead of methyl pyridium chloride being added as a brighteningagent 0.1 g./l. of-diamino pyridine was used. The cathode curent densitywas amperes per square foot and the anode current density was about 250amperes per square foot. A platinum anode was used instead of thechromium-iron alloy. Otherwise, operating conditions were about thesame.

The coating was found to comprise about 85 percent chromium and 15percent iron. The appearance of the resulting plate was setnibright andsmooth.

Example III Example IV A bath was prepared similar to that used inExample I except that instead of methyl pyridium chloride being added asa brightening agent 1.0 percent by volume formamide was used. Thecathode current density was about 100 amperes per square foot while theanode current density was about 250 amperes per square foot. A platinumanode was used. Otherwise, operating conditions were about the same. I

The coating was found to comprise about 85 percent chromium and 15percentiron. The appearance of the resulting plate was semibright andsmooth.

Example "V i A similar deposit of about 94 percentchromium Patented Feb.4, 1958 3. the'balance-iron-was obtained fronrthefollowingaqueoussolution: I

The urea was the supplementary brightening agent. Thebath'wa'smaintainedat a temperatureof'from 115 F. to 118 F., with a pHof from 1.9 to 2.0. The anode was made of a chromium-iron alloy. Thecathode current density wasfrom 300 to 400 amperes per square foot whiletheanode current density was approximately 100 amperes per square foot.The cathode efiiciency was from .26 to 34 percent.

The resulting plate exhibited asemibright and smooth surface.

Example VI A deposit of about 75 percent chromium and 25 percent ironwas obtained from the following aqueous solution:

GI/l. Basic chromium sulfate [Cr (SO -Na O-5H O]' 450 Ferrous sulfate[Fe (SO -7H Ol l Urea 188 The urea was the supplementary brighteningagent. The bath was maintained at 115 F. and thepl-i maintained at from1.7 to 2.0. The anode was made of a chromiumiron alloy (85% Cr, 15% Fe).The cathode. current density was from 300 to 400 while the anode currentdensity was about 100 amperes per square foot. The cathode efiiciencywas from 22 to 26 percent.

The resulting plate exhibited a bright surface. Hardness measurementstaken on samples from this bath ranged from 770 to 1098 Knoop.

Example VII A bathwaspreparedsimilar-to that used in Example VI except50 g./l. of ammonium sulfate were added and 0.3 g./l. ofdimethylthiourea was used in place of the urea. The temperature wasmaintained at 130 Fi'and the pH adjusted to from 1.5 to 1.8.

Eicample VIII A deposit of about-85 percent chromiumiandli percent ironwas obtained. from. the followingsolution:

Basic chromium. sulfate..[Cr (SO -Na O-5H O] 450 Ammonium sulfate [(NHQSOJ 50 Ferrous. ammoniumsulfate [FeSO (NI-19 80 6H O] 10 Boric acid [HBO 30.

Dimethyl urea ,4.0

Example IX A deposit of approximately-98rpercent chromium and twopercent nickel was. obtained. from the following aqueous-"solutionsGtll." Chromium ammonium sulfate [Cr (SO (NI-l SO -24H O] 300 Ammoniumsulfate [(NH.;) 80 150 Nickel sulfate [NiSO -(NH SO -6H O] 1.5 Sodiumsalt of sulfonated-saccharin 2 The sodiumsalfof sulfonated saceharin wasthe supplementany brightening agent. The, bath .was maintained.at.about.115 F.,- anduthepH;wasmaintained atfrom 1.4 to 1.5.. Theanodewas-, madei. of platinum. The cathode current density was from to 250amperes per square footand ,the anode, current density was up to 1000amperes per square foot. The leveling action was about 40 percentper..0.0005- inch of plate;

The resulting plate was semibright and smooth.

Example A bath was prepared similar to that used in Example. IX exceptthat, instead of 2 g./l. of sodium salt of sulfonated saccharin beingused, 4 g./l. were used. Also. 3 g./l. instead of 1.5 g./l. of nickelsulfate were added. The pH was maintained at 1.6, and the cathodecurrent density, maintained at 250 amperes per square foot. Otherwise,operating conditions were the same.

The resulting plate comprised about 98 percent chm-.- mium and twopercent nickel. and exhibited a mirrorbright surface that was verysmooth.

Example XI A bath was prepared similar to that used in Example IX exceptthat, instead of sodium salt of sulfonated saccharin. being, used as abrightening agent 0.5 g./l. of methyl pyridium chloride was used. Also 3g./l. instead. of. 1.5 g./1. of nickel sulfate were added. The pH was,maintained at 1.0. The cathode current density was,125 amperes persquare foot and the anode current density was 500 amperes per squarefoot. Otherwise, operating conditions were the same.

The resulting plate comprised about 98 percent chromium and two percentnickel and exhibited amirrorbright surface that was smooth.

Example XII A bath was prepared similar to that used in Example IXexcept that, instead of sodium salt of sulfonated saccharin being usedasa brightening agent 0.5 g./l. of histidine. monohydrochloride was added.The pH was maintainedat 1.6. The cathode current density was amperes persquare foot and the anode current density was 600 amperes per squarefoot. Otherwise,,operating.v conditions were the same.

Theresulting plate comprised about 98percent chromium and 'two percentnickel and exhibited a semibrig'ht, smooth surface.

Incarrying'out most ofthe plating operations, glass tanks were'used.However, it should be obvious that any material can, be used thatwillnotreact with the electrolyte, during I the. plating process. Rubber-linedsteel tankshave provided to be satisfactory.

Chromium-alloy plates maybe obtainedgfrom these baths'bymsingapH'of fromabout 0.2to about 3.5; how.- ever, to obtainthe--best results, thepreferredrange is from about1.4'to'2.5.'- The pH maybe adjusted byadding acid or alkaline reagents such'as sulfuric acid or ammoniumhydroxide, to the solutions; Plating baths made up of chromium ammoniumsulfate; chromium potassium sulfate; chromium sulfate,- are-acid-innature and require initialadditions of alkalihe.reagents,. such asammonium hydroxidedoobtain:the-properpH. Trivalent chromium hathsmadewp,lfromtbasic. chromium; sulfate. chromium.

carbonate. and. chromium oxide; require acid additions to .obtainthepproperin-itialpH. During. operat on of thee baths cithenthose in.which :C lIOml mQmmDDlD IL Qlc' fate.or other. trivalent,chromiumcomppunds,have.been.

addediitmaybe necessary toadd small amounts of acid to prevent the pHfrom rising. Boric acid may be added to the baths as a buffer reagent tostabilize the pH. If alkaline reagents, such as ammonium hydroxide, areadded to the bath after it has been prepared, special care should betaken to avoid the formation of precipitates which are relativelyinsoluble.

The addition agents or brightening additions of this invention may beany of the principal organic ammonia derivatives or mixtures of theprincipal organic ammonia derivatives. By principal organic ammoniaderivatives is meant any organic amine or amide. Best results areobtained by making additions of methyl pyridine chloride, diaminopyridine, formamide, urea, dimethylthiourea, histidinemonohydrochloride, and sulfonated saccharin.

While satisfactory results can be obtained by additions of any of thepreferred compounds over a range of from a trace to the saturation pointof the brightening agent, best results are obtained by maintaining theconcentration at from 0.1 to g./l. In the case of urea, there appears tobe no preferred range in that additions of from 0.1 to 180 g./l. areeffective.

Trivalent chromium ions can be supplied to the plating baths by theaddition of trivalent chromium compounds, such as chromium ammoniumsulfate, chromium sulfate, basic chromium sulfate, chromium carbonate,chromium potassium sulfate, and chromic oxide. The amount of trivalentchromium ions used in the baths is dependent on the current density andthe temperature at which the bath is operated. Satisfactory results havebeen obtained with concentrations ranging from g./l. to saturation.However, the most satisfactory results are obtained with concentrationsof from 30 to 75 g./l. If chromic oxide or chromium carbonate are usedas the source of trivalent ions, additions of a sulfuric acid arenecessary to provide sulfate ion concentrations which, for best results,should not be less than 80 g./l. If chromium potassium sulfate is used,the potassium ion concentration should not exceed 150 g./l.

Trivalent chromium salts are commercially prepared by reducing chromicacid or sodium dichromate with an organic reducing agent such asalcohol, molasses, or with sulfur dioxide. The product contains residualreducing agents, and oxidation products thereof, since an excess of thereducing agent is used to complete the reduction. Thus, plain solutionsmade up of trivalent chromium salts will contain these harmfulimpurities. The excess reducing agents, and oxidizing products thereof,and any other harmful impurities in the bath can be removed by theaddition of a small amount of activated carbon, preferably by means of aslurry of the finely divided powder in Water. The activated carbonremoves the impurities by means of absorption. The purification of theplating baths by means of activated carbon results in smoother andbetter plates.

The alloying constituents of the plating baths are added to the bath inthe form of metal salts such as iron or nickel sulfate. The valence ofthe alloying metals is not as important a factor in the resulting plateas is the valence of the chromium. For instance, iron may be addedeither as ferrous or ferric ammonium sulfate, ferrous or ferric sulfate,or by means of a mixture of ferrous and ferric salts. However, for bestresults, the reduced or ferrous salts are preferred. Nickel, as analloying element may be added as nickel sulfate or nickel ammoniumsulfate. The amount of alloying metal ions added to the bath isdependent on the composition of the alloy plates desired. Alloy platescan be produced that are predominantly iron or nickel in composition;however, by combining the ferrous or ferric ion. concentrations to from0.6 to 2.5 g./l., of the nickel ions to from 0.1 to 1.0 g./l., betteralloy plates are obtained.

While the examples heretofore given have related only to chromium-ironand chromium-nickel alloys, the electroplating baths of this inventionmay-also be readily 6 adapted to chromium-cobalt alloys. To electroplatea chromium-cobalt alloy, cobalt salts, such as cobaltammonium sulfate,can be substituted for the ferrous or nickel compounds in the platingsolution. The preferred range for cobalt ions is substantially the sameas the preferred range for nickel, that is from 0.1 to 1.0 g./l.

Various ternary or even quaternary combinations of these metals can beelectrodeposited in the form of hard alloy plates. For example, a brightchromium-iron-nickel alloy or a bright chromium-iron-cobalt alloy can beelectrodeposited by means of the electroplating baths of this invention.Nickel or cobalt salts or both nickel and cobalt salts are added to thebath in addition to iron salts and trivalent chromium compounds toobtain ternary or quaternary bright alloy plates.

Alkali metal compounds are added to the bath to ob tain. improvedthrowing power. The term alkali metal compound is intended to includeammonium compound. Ammonium sulfate and sodium sulfate have proved to besatisfactory when used for this purpose, but other alkali metalcompounds, such as potassium sulfate may be used as well. Ammoniumcompounds have proved to be the most effective for this purpose. Thealkali metal compounds may be added separately or as mixtures. Additionof alkali metal compounds are particularly effective when plating isdone with low current density and low concentrations of trivalentchromium ions. Concentration of the alkali metal compounds in theplating bath are dependent, to some extent, on the trivalent chromiumsalt or compound used. For instance, when using basic chromium sulfate,sufficient sodium sulfate may be present in the bath after dissolvingthis chromium salt to carry on the plating operation with furtheradditions of alkali metal compounds. For best results, total alkalimetal ion concentration should be within the concentration range of from10 to 50 g./l. In baths where sulfate salts are employed, total sulfateion concentrations should be within the range of from to 600 g./l.

The plating bath may be operated over a wide range of temperaturesproviding the pH is properly adjusted. There is some danger of chromealum or chromium ammonium sulfate precipitating from the bath where theconcentration of the chromium is in excess of 70 g./l. and thetemperature is allowed to drop below F. The preferred temperature rangefor the trivalent chromium baths of this invention is from 110 F. to F.

Satisfactory plating has been obtained by using current densities offrom 100 to 600 amperes per square foot. The selection of the propercurrent density is dependent upon the concentration of the chromium andalloy salts. Other factors alfecting the choice of the proper currentdensity include the size of the plating tank, the shape and contour ofthe parts, and the time required to produce a given thickness.

The anode may be made of any material that will conduct an electriccurrent and that will not react with the plating bath to adverselycontaminate the plating solutions. It is preferable to use eitherchromium alloy anodes corresponding to the desired plate composition, orplatinum, or platinum-covered silver anodes. When using chromium alloyanodes, either chromium-iron alloy or chromium-nickel alloy, it ispreferable to adjust the anode current density to between 50 and 100amperes per square foot. By this means, the metal is dissolved from theanodes at the same rate as metal is deposited on the cathodes. Ifplatinum or platinum-covered silver anodes are used, the anode currentdensity is not critical and may be between 50 and 1000 amperes persquare foot.

When insoluble anodes are used, such as a platinum anode describedabove, the bath is not replenished in chromium or the alloy metal. As aresult of continuous operation, the concentration of the chromium andthe alloying metal will diminish proportionally with the time ofelectrodeposition, These metals must be constantly 7 replaced byaddition of metal; compounds, such as, the trivaleng chromium salts orcompounds originallyv .used, and theiralloying salts or solublemetal,,oxi de,or hyiali -x It will, of course, be understood thatthevarious details of the process may bevaried without departingfrom theprinciples of this invention.

What is claimed is;

1. The method of electrodepositing a bright; chromiumiron. alloy platewhich comprises electrolyzingian aqueous bath containingfrom 30 to 75g./1. oftrivalentchrorninm ions, 10. to 50 ,g./l. of alkali metal ions,0.6 to 2.5 g./ l. of; ironaions, and containing additionally atileastone brightening agent in the range specified selected from the groupconsisting of:

Brightening agent:

. Methyl pyridium chloride Diamino pyridine Formarnide .1+ 10Dimethylthiourea .1 .10 Histidine monohydrochloride ,1 10 Sulfonatedsaccharin, .1-, 10

2. Themethodof electrodepositinga bright chromiumnickel alloys platewhich comprises electrolyzingan: aqueous' bath-containing from 30 to 75g./l. of -trivalent chromium-ions, 10m 50 g./l.of-alkali metal=ions, 0.1to-1.0 g. /l. of nickel ionsand containing additionallyat least onebrightening agent in -the range specified selected from the groupconsistingof:

Brightening agent: Range g. l. 7 Methyl pyridium chloride 1- 1O iam py dnea -i-a-r----as----- 1. 10

Formamide .1' 10 Dimethylthiourea l- 10 Histidine monohydrochloridm" .110 Sulfonated saccharin .1- 10 3. The-method of'electrodepositing abright chromiumcobalt--alloy platewhich comprises electrolyzing anaqueousbath containing from 30-to 75 g./l. of trivalentchromium ions, 10to-50 g./l. of-alkali metal;ions,- 0.1 to 1.0 g.-/l. of cobalt ionsand'containing additionally at least one brightening agent inthe range;specified selected fromthe groupconsistingof:

Range gy l.

4..A composition ofi matters-for 'electrodepositingi-a chromium-ironalloy platev which "comprises; an 1 aqueousbath: containing from=30 toJSg/l. oftrivalentchromium' ions, :10 to 50.g./l; ofalkalimetaltions, 0.6to 2.5 g./l;- of. iron ions, and containing additionally-atleastonebrightening agent in the rangespecified selected fromthegroupconsisting of:

5."A compositijon ofgmatter for electrodepositing aw chromium-nickelalloy plate which comprises an aqueous bath containing from 30 to g./l.of trivalent chromiums.

ions,; 10 to; 5 0 g. /l. of alkali metal ions, 0.1 to- 1.0 g./l; ofnickel ions, and; containing additionally at least one brighteningagentin therange specified selected fromthe group consisting of:

6.-A-con1position of matter for electrodepositing a chromium-cobaltalloyplatewhich comprises an aqueous bath containing from 30 t0'75-g./l.of trivalent chromium ions, 10-to-50 g./l.- of-alkali metal-ions, 0.1to1.0 g./l. of cobalt ions andcoutaining additionally at least onebrighteningagentin-the range specified selected from the groupconsisting of:

e inaagent: Range e U395; i Methyl pyridium:chloride .1-10 Diamino;pyridine, .1-10 Formamid e- .1-10 Dimethylthiourea .110 Histidine,monohydrochloridea .1-10 Su-lfona ted; saccharin .l-lO

7. The method of ,electrodepositing a brightchromiumalloyplate,,which,comprises electro1yzing an; aqueous bathcontainingfil) to75 g./ l. of trivalent chromium ions,

10m 50 g./l. of alkali metal ions, the ions of at least, onealloying-.metal selected from the .group, consisting of from, 0.6 .,,to,2.5 ,g./l., of iron ions, from- 0.1 to 1.0,

g./l. of nickel ions, from ,0.1 to 1.0 g./l. ofcobalt ions,:, andcontaining additionally at least one brighteningagent in the rangespecified, selected from the group consisting of:

Brightening agent: Range g./l.

Urea .1-188 Methyl pyridium chloride .1-10 Diamino pyridine .1-10Formamide .1-10

Dimethylthiourea .1-10 I-listidine rnonohydrochloride .1-10 Sulfonatedsaccharin .l-10

8. A method of-electrodepositing a bright-chromiumalloy plate which:comprises= electrolyzingjan aqueous bath containing from-30 to 75 g./l.of trivalent chromium ions, 10 to 50 g./l. of alkali metal ions,the'ions of at leasbone alloyinggmetal selected from the group.consistingof from-0.6 to 2.5' g./l. of iron ions, from 0.1 to. 1.0 g./l.of nickel ions, and f1'om 0.1 to 1.0 g./l. of cobalt ions, andcontaining additionally from1 to 10 g./l. of sulfonated saccharin.

9. The method of electrodepositing a bright chromiumiron alloy platewhich'comprises electrolyzing an'aqueous bathcontainingfrom 30 to 75g./l. of trivalent chromium ions, 10 to 50 -g./1. of alkali metal ions,0.6 to 2.5 g./l.

of= iron; ions, and. containing additionally from .1 to 10 g./l. of,sulfonated saccharin.

lO The method of electrodepositing a bright chromiumnickel alloyplate-,whichcomprises electrolyzing an aqueous batlncontaining from 30to 75 g./1. of trivalent chromium ions,, lOotofil) ;g./ l. of alkali.metal ions,- 0.1 to 1.0 g./l.

Qflnickel ions,; and cpntaining additionally from .1 to 10 I of s lfonaed: cha in-i 11. The methodvof electrodepositing;a.bright;chromiumvcobaltalloy plate, whichvcomprises electrolyzing anaqueoushathcontainingfrom 30 to 75 g./ l. of trivalent chromium, ions, 10 to 50g./l. of alkali metal ions, 0.1 to 1.0 g./l.

9 of cobalt ions, and containing additionally from .1 to 10 g./l. ofsulfonated saccharin.

12. A composition of matter for electrodepositing a chromium-alloyplate, which comprises an aqueous bath containing 30 to 75 g./l. oftrivalent chromium ions, 10 to 50 g./l. of alkali metal ions, the ionsof at least one alloying metal selected from the group consisting offrom 0.6 to 2.5 g./l. of iron ions, from 0.1 to 1.0 g./l. of nickelions, and from 0.1 to 1.0 g./l. of cobalt ions, and containingadditionally at least one brightening agent in the range specified,selected from the group consisting of:

Brightening agent: Range g./l. Urea .l-188 Methyl pyridium chloride.1-10 Diamino pyridine .1-10 Formamide .1-10 Dimethylthiourea .1-10Histidine monohydrochloride .110 Sulfonated saccharin .1-10

13. A composition of matter for electrodepositing a chromium alloymaterial which comprises a conductive aqueous solution containing from30 to 75 g./l. of trivalent chromium ions, 10 to 50 g./l. of alkalimetal ions, the ions of at least one alloying metal selected from thegroup consisting of from 0.6 to 2.5 g./l. of iron ions, from 0.1 to 1.0g./l. of nickel ions, from 0.1 to 1.0 g./l.

10 of cobalt ions, and containing additionally from .1 to 10 g./l. ofsulfonated saccharin.

14. A composition of matter for electrodepositing a chromium-iron alloymaterial which comprises a conductive aqueous solution containing fromto 75 g./l. of trivalent chromium ions, 10 to g./l. of alkali metalions, from 0.6 to 2.5 g./l. of iron ions, and containing additionallyfrom .1 to 10 g./l. of sulfonated saccharin.

15. A composition of matter for electrodepositing a chromium-nickelalloy material which comprises a conductive aqueous solution containingfrom 30 to g./l. of trivalent chromium ions, 10 to 50 g./l. of alkalimetal ions, from 0.1 to 1.0 g./l. of nickel ions, and containingadditionally from .1 to 10 g./l. of sulfonated saccharin.

16. A composition of matter for electrodepositing a chromium-cobaltalloy material which comprises a conductive aqueous solution containingfrom 30 to 75 g./l. of trivalent chromium ions, 10 to 50 g./l. of alkalimetal ions, from 0.1 to 1.0 g./l. of cobalt ions, and containingadditionally from .1 to 10 g./l. of sulfonated saccharin.

References Cited in the file of this patent UNITED STATES PATENTS2,377,229 Harford May 29, 1945 2,655,471 Chester Oct. 13, 1953 2,704,273Yoshida Mar. 15, 1955 2,766,196 Yoshida Oct. 9, 1956 of the abovenumbered patent requiring U. S. DEPARTMENT OF COMMERCE PATENT OFFICECERTIFICATE OF CORRECTION Patent No, 2,822,326 February 4, 1958 WilliamH., Safranek appears in the printed specification It is hereby certifiedthat error correction and that the said Letters Patent should read ascorrected below.

Column 2, line 16, for "pridium read pyridium column 8, line 12, for"Diamino pyiuldine read Dimethglthiourea Signed and sealed this 25th dayof March 1958 (SEAL) Attest:

L Ho AXLINE KAR ROBERT C. WATSON Attesting Officer Conmissioner ofPatents

7. THE METHOD OF ELECTRODEPOSITING A BRIGHT CHROMIUMALLOY PLATE, WHICHCOMPRISES ELECTROLYZING AN AQUEOUS BATH CONTAINING 30 TO 75 G./L. OFTRIVALENT CHROMIUM IONS, 10 TO 50 G./L. OF ALKALI METAL IONS, THE IONSOF AT LEAST ONE ALLOYING METAL SELECTED FROM THE GROUP CONSISTING OFFROM 0.6 TO 2.5 G./L. OF IRON IONS, FROM 0.1 TO 1.0 G./L. OF NICKELIONS, FROM 0.1 TO 1.0 G./L. OF COBALT IONS, AND CONTAINING ADDITIONALLYAT LEAST ONE BRIGHTENING AGENT IN THE RANGE SPECIFIED, SELECTED FROM THEGROUP CONSISTING OF: